Word-line driver and method of operating a word-line driver

ABSTRACT

Word-line drivers, memories, and methods of operating word-line drivers are provided. A word-line driver coupled to an array of memory cells includes a decoder powered by a first power supply. The decoder is configured to decode an address to provide a plurality of word-line signals. The word-line driver also includes a plurality of output stages powered by a second power supply that is different than the first power supply. Each of the output stages includes a first transistor having a gate controlled by a first control signal and an inverter. The inverter is coupled between the first transistor and a ground and has an input coupled to the decoder to receive one of the word-line signals. The word-line driver also includes pull-down circuitry coupled between the gates of the first transistors and the ground and activated by a second control signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/725,460, filed Oct. 5, 2017, which claims priority to U.S.Provisional Patent Application No. 62/433,270, filed Dec. 13, 2016, bothof which are incorporated herein by reference in their entirety.

BACKGROUND

The present invention relates generally to semiconductor memory designs,and, more particularly, to a memory word-line driver design.

The core of a semiconductor memory comprises at least onetwo-dimensional memory cell array, where information is stored.Traditionally, word lines select rows, which activate cells, and bitlines select columns, which access (i.e., read or write) the cells. Whena word line and a bit line are activated, a particular memory cellconnected to them is selected.

To activate a word line, its voltage is normally set to a high voltage,which is equal to a positive supply voltage incomplimentary-metal-oxide-semiconductor (CMOS) circuitry. Setting a wordline to a low voltage, which is a voltage complimentary to the positivesupply voltage, de-activates the word line. While the low voltage iscustomarily set to ground, or 0 V, the value for the high voltage can bedifferent for various semiconductor manufacturing technologies. Forinstance, in a deep-sub-micron technology, a high voltage can be 1.2 Vor even lower, while in a sub-micron technology the high voltage can be2.5 V. But for a given memory chip and a given technology, the highvoltage is normally designed to a fixed value, and this is particularlytrue for CMOS memory circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a circuit diagram depicting a word-line driver, in accordancewith some embodiments.

FIG. 2 is a timing diagram showing signals of the word-line driver ofFIG. 1 in the time domain, in accordance with some embodiments.

FIG. 3 is a circuit diagram depicting an output stage of the word-linedriver of FIG. 1, in accordance with some embodiments.

FIG. 4 is a block diagram depicting a memory device including multiplearrays of memory cells, in accordance with some embodiments.

FIG. 5 is a flowchart depicting steps of an example method for operatinga word-line driver, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

FIG. 1 is a circuit diagram depicting a word-line driver 100, inaccordance with some embodiments. As seen in the figure, the word-linedriver 100 is coupled to n+1 word lines disposed to the left of theword-line driver 100, with these word lines being labeled WL_L[0]through WL_L[n]. The word-line driver 100 is also coupled to n+1 wordlines disposed to the right of the word-line driver 100, with these wordlines being labeled WL_R[0] through WL_R[n]. To drive the word lines,the word-line driver 100 includes a decoder and a plurality of outputstages 104.

The decoder includes multiple decoder logic modules 102 a, 102 b, 102 cand is configured to decode an input address to provide a plurality ofword-line signals. In embodiments, the input address to be decoded isprovided via a line SLPM_WL_XDEC shown in FIG. 1. Each of the decoderlogic modules 102 a, 102 b, 102 c includes multiple transistors, witheach of these transistors being relatively small in size, inembodiments. Due to their relatively small sizes, these transistorsconsume only a minimal amount of power and are not a significant sourceof leakage current.

Each of the decoder logic modules 102 a, 102 b, 102 c of the decoder iscoupled to one or more output stages 104. In the illustration of FIG. 1,only one output stage 104 is shown for each of the decoder logic modules102 a, 102 b, 102 c. The output stages 104 may also be referred to as“final stages” because they form the end of the word-line driver 100 andare coupled directly to the word lines. Each output stage of theplurality of output stages 104 includes a first transistor 101 having agate controlled by a first control signal SLPM_WL. In embodiments, thefirst control signal SLPM_WL is a sleep signal used to power down theoutput stages 104 in a standby mode of operation and to wake up theoutput stages 104 in an active mode of operation. The standby and activemodes are described in further detail below. Each of the output stages104 further includes an inverter 106 coupled between the firsttransistor 101 and a ground (e.g., Vss or GND). Specifically, in theembodiment of FIG. 1, the first transistor 101 comprises a p-typemetal-oxide-semiconductor (PMOS) transistor with a source terminalcoupled to a positive supply voltage (e.g., Vcc) and a drain terminalcoupled to the inverter 106. Details of the electrical connectionbetween the first transistor 101 and the inverter 106 are described infurther detail below with reference to FIG. 3.

The inverter 106 has an input coupled to a decoder logic module toreceive one of the word-line signals generated by the decoder. Theinverter 106 generates an output that is an inverted version of theword-line signal input, and the output is used to drive a word linecoupled to the inverter 106. In embodiments, the word-line driver 100 iscoupled to a memory array of a memory chip (not shown in FIG. 1) thatoperates in both active and standby modes. In the active mode ofoperation, the memory array is being actively accessed (i.e., read fromor written to), and an output stage of the output stages 104 provides acurrent source to (i) pull up a corresponding word line to a highvoltage when the word line is selected, and (ii) pull down the word lineto a low voltage when the word line is not selected. In embodiments, thehigh and low voltages are predetermined voltage values (e.g., positivesupply voltage and ground, respectively). By contrast, in the standbymode, the memory chip is not being actively accessed, and the outputstage clamps the word-line voltage to a predetermined low voltage.

In embodiments of the present disclosure, each of the output stages 104includes multiple transistors that are relatively large in size, incomparison to the relatively small transistors of the decoder logicmodules 102 a, 102 b, 102 c. Thus, for instance, the first transistor101 is a relatively large transistor, and the inverter 106 likewiseincludes one or more relatively large transistors, in embodiments. Inconventional word-line drivers, the relatively large transistors of theoutput stage form a large leakage path in the standby mode of operation.Leakage current that flows through the leakage path results in arelatively large amount of undesirable leakage power in the standbymode.

To address the leakage problem of the conventional word-line drivers,the word-line driver 100 of the present disclosure enables the outputstages 104 to be powered down (i.e., turned off) in the standby mode,thus providing a reduction of leakage power. When the memory chiptransitions to the active mode, the output stages 104 are powered up(i.e., turned on) in a relatively short amount of time to provide a fastwakeup. The aforementioned first control signal SLPM_WL is used to powerthe output stages 104 up and down. In embodiments, control circuitry 103controls the first control signal SLPM_WL to power the output stages 104up and down, depending on the mode of operation.

To enable the output stages 104 to have a fast wakeup when the memorychip transitions from the standby mode to the active mode, the word-linedriver 100 provides power to the decoder logic modules 102 a, 102 b, 102c and the output stages 104 using separate internal power supplies. Asseen in FIG. 1, the decoder logic modules 102 a, 102 b, 102 c of thedecoder are powered by a first power supply VDDHD_XDEC. By contrast, theoutput stages 104 disposed on the left- and right-hand sides of theword-line driver 100 are powered by second power supplies VDDHD_WL_L andVDDHD_WL_R, respectively. The second power supplies VDDHD_WL_L andVDDHD_WL_R are separate than and different from the first power supplyVDDHD_XDEC.

By using the different first and second power supplies to power thedecoder logic modules 102 a, 102 b, 102 c and the output stages 104,respectively, this helps to ensure that the output stages 104 have afast wakeup. Specifically, by using the separate power supplies, thesecond power supplies VDDHD_WL_L and VDDHD_WL_R used to power the outputstages 104 only experience a small voltage drop in the standby mode,thus enabling the output stages 104 to wake up relatively quickly whentransitioning from the standby mode to the active mode.

To illustrate this, reference is made to FIG. 2. This figure is a timingdiagram showing signals of the word-line driver 100 of FIG. 1 in thetime domain, in accordance with some embodiments. Specifically, thefigure shows the signals during standby modes 204, 208 and an activemode 206. During the standby modes 204, 208, the memory array is notbeing accessed, such that word-line voltages are clamped to apredetermined low voltage. The signal 201 (labeled “WL”) isrepresentative of a voltage of a word line and shows that the wordline's voltage is clamped low during the standby modes 204, 208. Duringthe active mode 206, selection of the word line causes the voltage ofthe word line to be pulled high, as illustrated by the signal 201.

In FIG. 2, the signal 202 (labeled “VDDHD_WL”) is representative of avoltage of one of the second power supplies VDDHD_WL_L and VDDHD_WL_R ofFIG. 1. As seen in the figure, the signal 202 has a voltage in thestandby modes 204, 208 that is nearly equal to its voltage in the activemode 206. Because the voltage used to power the output stages 104 isonly slightly less in the standby mode than it is in the active mode,this enables the output stages 104 to wake up relatively quickly whentransitioning from the standby mode to the active mode. This is achievedthrough the use of the different first and second power supplies topower the decoder logic modules 102 a, 102 b, 102 c and the outputstages 104, respectively. As explained above, the decoder logic modules102 a, 102 b, 102 c of the decoder are powered by the first power supplyVDDHD_XDEC, and the output stages 104 disposed on the left- andright-hand sides of the word-line driver 100 are powered by second powersupplies VDDHD_WL_L and VDDHD_WL_R, respectively. By using the differentfirst and second power supplies to power the decoder logic modules 102a, 102 b, 102 c and the output stages 104, respectively, the secondpower supplies VDDHD_WL_L and VDDHD_WL_R used to power the output stages104 have a voltage in the standby modes 204, 208 that is nearly equal tothe voltage in the active mode 206. This enables the output stages 104to wake up relatively quickly when transitioning from the standby modeto the active mode.

With reference again to FIG. 1, the word-line driver 100 furtherincludes pull-down circuitry that includes second transistors 108, 110,112, 114. As explained below, the pull-down circuitry, along with theuse of the different power supplies to power the decoder logic modules102 a, 102 b, 102 c and the output stages 104, helps to ensure that theoutput stages 104 have a fast wakeup. The second transistors 108, 110,112, 114 of the pull-down circuitry are coupled between the gates of thefirst transistors 101 and ground.

In the embodiment of FIG. 1, each of the second transistors 108, 110,112, 114 is an n-type metal-oxide-semiconductor (NMOS) transistor with adrain terminal coupled to the gates of the first transistors 101 and asource terminal coupled to ground. Further, each of the secondtransistors 108, 110, 112, 114 includes a gate controlled by a secondcontrol signal SLPMB_WL. The second control signal SLPMB_WL is used toactivate the pull-down circuitry, with the activation of the pull-downcircuitry resulting in gate voltages of the first transistors 101 beingpulled to a low voltage (e.g., ground). Pulling the gate voltages of thefirst transistors 101 low in this manner helps to wake up the outputstages 104 more quickly. In embodiments, the control circuitry 103controls the second control signal SLPMB_WL to activate the pull-downcircuitry.

To illustrate use of the pull-down circuitry to wake up the outputstages 104 more quickly, reference is made again to FIG. 2. As notedabove, the first transistors 101 have gates controlled by the firstcontrol signal SLPM_WL, with the first control signal SLPM_WL being asleep signal used to power down the output stages 104 in the standbymode and to wake up the output stages 104 in the active mode. In FIG. 2,the signal 210 (labeled “SLPM_WL”) is representative of a voltage of thefirst control signal SLPM_WL. As seen in the figure, during the standbymode 204, the signal 210 has a high voltage (e.g., positive supplyvoltage or Vcc). The high voltage received at the gates of the firsttransistors 101 causes the first transistors 101 to be turned off duringthe standby mode, thus reducing the amount of leakage current in theoutput stages 104. During the transition from the standby mode 204 tothe active mode 206, the signal 210 transitions from the high voltage toa low voltage (e.g., ground). The low voltage received at the gates ofthe first transistors 101 causes the first transistors 101 to be turnedon during the active mode, such that current flows through them.

The pull-down circuitry enables the signal 210 to transition from thehigh voltage to the low voltage more quickly. In FIG. 2, the signal 212(labeled “SLPMB_WL”) is representative of a voltage of the secondcontrol signal SLPMB_WL received at the gates of the second transistors108, 110, 112, 114 of the pull-down circuitry. As seen in the figure,during the standby mode 204, the signal 212 has a low voltage. In theembodiment of FIG. 1, where the second transistors 108, 110, 112, 114are NMOS transistors, the low voltage causes these transistors to beturned off. During the transition from the standby mode 204 to theactive mode 206, the signal 212 transitions from the low voltage to ahigh voltage. The high voltage received at the gates of the secondtransistors 108, 110, 112, 114 causes these transistors to be turned onduring the active mode, such that current flows through them.

When this current flows through the second transistors 108, 110, 112,114 in the active mode 206, the drain terminals of these transistors arepulled to the low voltage (e.g., ground). Because the gates of the firsttransistors 101 are electrically coupled to the drains of the secondtransistors 108, 110, 112, 114, as explained above, this causes the gatevoltages of the first transistors 101 to be pulled to the low voltage aswell. Accordingly, this enables the sleep signal SLPM_WL received at thegates of the first transistors 101 to transition from the high voltageto the low voltage more quickly upon entering the active mode 206, suchthat the output stages 104 have a faster wakeup.

With reference again to FIG. 1, the second transistors 108, 110, 112,114 of the pull-down circuitry are spatially arranged and electricallyconnected in a manner that further facilitates the fast wakeup of theoutput stages 104. As seen in FIG. 1, the second transistors 108, 110,112, 114 are positioned at the top and bottom edges of the cell, abovethe first row of the word-line driver 100 and below the last row of theword-line driver 100. With this arrangement, the second transistors 108,110, 112, 114 of the pull-down circuitry pull the sleep signal SLPM_WLto the low voltage from both ends of its line, effectively decreasingthe line to half of its size and enabling the sleep signal SLPM_WL totransition to the low voltage faster for a faster wakeup of the outputstages 104.

Further, the second control signal SLPMB_WL used to active anddeactivate the pull-down circuitry is only received at the secondtransistors 108, 110, 112, 114 and is not received at the firsttransistors 101 of the output stages 104. By contrast, the first controlsignal SLPM_WL is received at each of the first transistors 101. Becausea number of the second transistors 108, 110, 112, 114 is less than anumber of the first transistors 101, the second control signal SLPMB_WLactivates the second transistors 108, 110, 112, 114 prior to the firstcontrol signal SLPM_WL activating the first transistors 101.Accordingly, this enables the second transistors 108, 110, 112, 114 tobegin pulling down the gate voltages of the first transistors relativelyquickly, further enabling the fast wakeup of the output stages 104.

As explained above, the output stages 104 of the word-line driver 100are powered down in the standby mode in order to reduce leakage power.By contrast, in embodiments, the decoder logic modules 102 a, 102 b, 102c of the decoder remain active and are not powered down in the standbymode. The decoder logic modules 102 a, 102 b, 102 c can remain poweredup at all times (i.e., in both standby and active modes) because eachincludes the relatively small transistors that consume only a relativelysmall amount of leakage power while in the standby mode. Further, bykeeping the decoder logic modules 102 a, 102 b, 102 c powered up duringthe standby mode, this ensures that timing characteristics (e.g., set-uptime) of the word-line driver 100 are not adversely affected.

Specifically, in embodiments, a clock generation circuit (not depictedin FIG. 1) transmits a clock signal to the word-line driver 100, and theword-line driver transitions from the standby mode to the active mode inresponse to a rising edge of the clock signal. With reference again toFIG. 2, the signal 214 is representative of the clock signal andillustrates that the rising edge of the clock signal triggers thetransition from the standby mode 204 to the active mode 206. Upon therising edge of the signal 214, the signal 210 representative of thevoltage of the first control signal SLPM_WL begins transitioning fromhigh to low in order to wake up the output stages 104. As explainedabove, the decoder logic modules 102 a, 102 b, 102 c of the decoder areconfigured to decode an input address to provide word-line signals fordriving word lines. For proper timing, the input address should bedecoded prior to waking up the output stages 104 (i.e., the decodingshould occur prior to the transition from the standby mode to the activemode). To ensure that this is the case, the decoder logic modules 102 a,102 b, 102 c of the decoder remain active at all times and are notpowered down in the standby mode.

The word-line driver 100 of FIG. 1 achieves a lower leakage power thanconventional word-line drivers without sacrificing speed or havingadverse effects on timing characteristics. As described above, theoutput stages that are the source of significant leakage power inconventional designs are powered down during the standby mode in theword-line driver 100 of FIG. 1, thus providing a substantial reductionin the leakage power. To ensure that the output stages 104 have a fastwakeup when transitioning from the standby mode to the active mode, theword-line driver 100 utilizes separate power supplies for the decodingmodules 102 a, 102 b, 102 c and the output stages 104, as explainedabove. Fast wakeup is further ensured through the use of the pull-downcircuitry including the second transistors 108, 110, 112, 114.Additionally, by keeping the decoding modules 102 a, 102 b, 102 c of thedecoder powered up during the standby mode, this ensures that timingcharacteristics of the word-line driver 100 are not adversely affected.

As explained above, each of the output stages 104 includes multipletransistors that are relatively large in size. These transistors includethe first transistor 101 (described above) and additional transistorsused to form the inverter 106. To illustrate the transistors of a singleoutput stage of the output stages 104, reference is made to FIG. 3. Thisfigure is a circuit diagram depicting an output stage of the word-linedriver of FIG. 1, in accordance with some embodiments. FIG. 3 depictsthe first transistor 101 and additional transistors 302 and 304 thattogether form the inverter 106. In the embodiment of FIG. 3, the firsttransistor 101 is a PMOS transistor having a source terminal coupled toa positive supply voltage (e.g., Vcc), a drain terminal coupled to asecond power supply VDDHD_WL (e.g., one of the second power suppliesVDDHD_WL_L and VDDHD_WL_R of FIG. 1), and a gate controlled by the firstcontrol signal SLPM_WL.

Further, in the embodiment of FIG. 3, the transistor 302 is another PMOStransistor having a source terminal coupled to the drain terminal of thefirst transistor 101, a drain terminal coupled to a word line (labeled“WL”), and a gate controlled by one of the word-line signals (labeled“WLB”) generated by the decoder. The transistor 304 is a NMOS transistorhaving a drain terminal coupled to the drain terminal of the transistor302, a source terminal coupled to ground, and a gate controlled by theword-line signal. Because the transistors 302 and 304 are coupledtogether to form an inverter, the word-line signal received as an inputis inverted to generate the output used to drive the word line.

The first transistor 101 controls the power to the transistors 302 and304 of the inverter 106, thus enabling the inverter 106 to be powereddown in the standby mode and powered up during the active mode.Specifically, the first transistor 101 includes the gate controlled bythe first control signal SLPM_WL. When the first control signal SLPM_WLis high during the standby mode, the first transistor 101 is turned off,and no current flows through the transistors 101, 302, and 304. Bycontrast, when the first control signal SLPM_WL is low during the activemode, the first transistor 101 is turned on, and current flows throughthe transistors 101, 302, and 304.

FIG. 4 is a block diagram depicting a memory device 400 includingmultiple arrays of memory cells, in accordance with some embodiments.The memory device 400 includes a first word-line driver 402 disposedbetween first and second arrays of memory cells 404, 406. Each of thearrays of memory cells 404, 406 includes a plurality of memory cells(e.g., static random access memory (SRAM) cells, dynamic random accessmemory (DRAM) cells, etc.) arranged in rows and columns. Word linesWL_L_TOP[0]-[n] and WL_R_TOP[0]-[n] select rows of the respective arrays404, 406, and bit lines (not illustrated in FIG. 4) select columns.

The first word-line driver 402 is the same as or similar to theword-line driver 100 of FIG. 1, in embodiments. Thus, the signals,lines, and power supplies depicted in FIG. 4 (i.e., VDDHD_WL_L,SLPM_WL_XDEC, VDDHD_XDEC, SLPM_WL, SLPMB_WL, and VDDHD_WL_R) should beunderstood as being the same as those described above with reference toFIG. 1. The first word-line driver 402 is configured to drive the wordlines WL_L_TOP[0]-[n] and WL_R_TOP[0]-[n] to which it is coupled. Thelocal control 103 (also described above with reference to FIG. 1)includes control circuitry configured to control operation of the firstword-line driver 402. Specifically, the local control 103 controls oneor more of VDDHD_WL_L, SLPM_WL_XDEC, VDDHD_XDEC, SLPM_WL, SLPMB_WL, andVDDHD_WL_R to direct the operation of the word-line driver 402. Inembodiments, for example, the local control 103 controls the voltage ofthe first control signal SLPM_WL to power the output stages 104 up anddown, depending on the mode of operation. Likewise, in embodiments, thelocal control 103 controls the voltage of the second control signalSLPMB_WL to activate the pull-down circuitry and facilitate fasterwakeup of the output stages 104.

The memory device 400 further includes a second word-line driver 414disposed between third and fourth arrays of memory cells 416, 418. Wordlines WL_L_BOT[0]-[n] and WL_R_BOT[0]-[n] select rows of the respectivearrays 416, 418. The second word-line driver 414 is the same as orsimilar to the word-line driver 100 of FIG. 1, in embodiments, and isconfigured to drive the word lines WL_L_TOP[0]-[n] and WL_R_TOP[0]-[n]to which it is coupled. The local control 103 controls operation of thesecond word-line driver 414 in a manner similar to its control of thefirst word-line driver 402.

Global control 424 is the main control block of the memory device 400,in embodiments. The global control 424 uses control inputs received fromthe outside world (e.g., chip-level inputs) and generates appropriateinternal signals to perform requested operations. In embodiments, theglobal input/outputs (IOs) 420, 422 are disposed alongside the globalcontrol 424 and near the boundary of the memory device 400, asillustrated in FIG. 4. The global I/Os 420, 422 are coupled to theoutside world, allowing a device (e.g., a processor, chip, etc.) to readfrom the memory device 400 and/or write to the memory device 400. Thus,in reading data from the memory device 400, data is read from the arrays404, 406, 416, 418 and transmitted to one or more of the global I/Os420, 422, enabling the data to be received by the device. Likewise, inwriting data to the memory device 400, the device transmits the data toone or more of the global I/Os 420, 422, enabling this data to bewritten to the arrays 404, 406, 416, 418. In embodiments, there is oneglobal IO block for each bit of the memory's word size.

The local control 103 and local IOs 410, 412 are present in a memorydevice including multiple arrays of memory cells, as in the example ofFIG. 4. The local control 103 includes circuitry that operates onsignals received from the global control 424 and generates other signalsto perform requested operations. For example, based on signals receivedfrom the global control 424, the local control 103 generates signals toactivate a certain word-line driver coupled to one of the arrays 404,406, 416, 418. Further, in embodiments, based on signals received fromthe global control 424, the local control 103 generates signals sent tothe local IOs 410, 412.

In a memory device including multiple arrays of memory cells, as in FIG.4, the local IOs 410, 412 are disposed alongside the local control 103.The local IOs 410, 412 interface with bitlines from both the uppermemory cell arrays 404, 406 and the lower memory cell arrays 416, 418.Further, the local IOs 410, 412 operate on control signals from thelocal control 103 and perform appropriate operations on selectedbitlines (e.g., read or write data). The local IOs 410, 412 alsointerface with the global IOs 420, 422. Specifically, in embodiments,the local IOs 410, 412 (i) receive data to write from the global IOs420, 422, and (ii) send data read from the arrays 404, 406, 416, 418 tothe global IOs 420, 422.

FIG. 5 is a flowchart depicting steps of an example method for operatinga word-line driver, in accordance with some embodiments. FIG. 5 isdescribed with reference to FIG. 1 above for ease of understanding. Butthe process of FIG. 5 is applicable to other hardware arrangements aswell. At 502, power is provided to a decoder (i.e., a decoder includingdecoder logic modules 102 a, 102 b, 102 c) of the word-line driver(i.e., word-line driver 100) using a first power supply (i.e., firstpower supply VDDHD_XDEC). At 504, an address (i.e., an address providedvia line SLPM_WL_XDEC) is decoded using the decoder to generateword-line signals.

At 506, the word-line signals are transmitted to a plurality of outputstages (i.e., output stages 104) of the word-line driver, where theplurality of output stages control voltage levels of word lines (i.e.,word lines WL_L[0]-[n] or WL_R[0]-[n]) based on the word-line signals.The plurality of output stages are powered by a second power supply(i.e., second power supply VDDHD_WL) that is different than the firstpower supply. At 508, the plurality of output stages are turned off whentransitioning from an active mode of operation to a standby mode ofoperation. In any of the methods disclosed herein, one or more of thedescribed operations may omitted, and other operations may be added.Further, in any of the disclosed methods, the order of operations mayvary from what is described herein. Thus, for instance, the operations502, 504, 506, 508 of FIG. 5 need not be performed in the order shown inthe figure.

The present disclosure in various embodiments is directed to word-linedrivers, memories, and methods of operating word-line drivers. Anexample word-line driver coupled to an array of memory cells includes adecoder powered by a first power supply. The decoder is configured todecode an address to provide a plurality of word-line signals. Theword-line driver also includes a plurality of output stages powered by asecond power supply that is different than the first power supply. Eachof the output stages includes a first transistor having a gatecontrolled by a first control signal and an inverter. The inverter iscoupled between the first transistor and a ground and has an inputcoupled to the decoder to receive one of the word-line signals. Theword-line driver also includes pull-down circuitry coupled between thegates of the first transistors and the ground and activated by a secondcontrol signal.

In another example, a memory includes an array of memory cells and aword-line driver configured to drive word lines coupled to the array ofmemory cells. The word-line driver includes a decoder configured todecode an address to provide a plurality of word-line signals. Theword-line driver also includes a plurality of output stages, each of theoutput stages having an input coupled to the decoder to receive one ofthe word-line signals. The word-line driver further includes controlcircuitry configured to turn off the plurality of output stages in astandby mode during which the array of memory cells is not beingaccessed.

In an example method for operating a word-line driver, power is providedto a decoder of the word-line driver using a first power supply. Anaddress is decoded using the decoder to generate word-line signals. Theword-line signals are transmitted to a plurality of output stages of theword-line driver. The plurality of output stages control voltage levelsof word lines based on the word-line signals and are powered by a secondpower supply that is different than the first power supply. Theplurality of output stages are turned off when transitioning from anactive mode of operation to a standby mode of operation.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A word-line driver coupled to an array of memorycells, the word-line driver comprising: a decoder powered by a firstpower supply and being configured to decode an address to provide aplurality of word-line signals; a plurality of output stages powered bya second power supply that is different than the first power supply,each of the output stages including a first transistor having a gatecontrolled by a first control signal; and pull-down circuitry coupledbetween the gates of the first transistors and the ground and activatedby a second control signal, the pull-down circuitry configured to pulldown gate voltages of transistors of the output stages to a low voltage.2. The word-line driver of claim 1, wherein the pull-down circuitrycomprises one or more second transistors coupled between the gates ofthe first transistors and the ground, each of the second transistorsincluding a gate controlled by the second control signal.
 3. Theword-line driver of claim 2, wherein a number of the second transistorsis less than a number of the first transistors.
 4. The word-line driverof claim 1, wherein the first transistor comprises a PMOS transistorcoupled to the second power supply; and the inverter comprises (i) asecond PMOS transistor coupled to the first PMOS transistor and having agate controlled by the one of the word-line signals, and (ii) a firstNMOS transistor coupled between the second PMOS transistor and theground.
 5. The word-line driver of claim 4, wherein the pull-downcircuitry comprises one or more second NMOS transistors coupled betweenthe gates of the first transistors and the ground, the one or moresecond NMOS transistors having gates controlled by the second controlsignal.
 6. The word-line driver of claim 1, wherein the inverter has anoutput electrically connected to a word line that is coupled to thearray of memory cells.
 7. The word-line driver of claim 1, wherein thefirst transistor is configured to provide power to the inverter based ona voltage of the first control signal.
 8. The word-line driver of claim1, wherein the decoder comprises a plurality of decoder logic modules,each of the decoder logic modules being coupled to one or more outputstages of the plurality of output stages.
 9. A memory comprising: anarray of memory cells; and a word-line driver configured to drive wordlines coupled to the array of memory cells and including: a decoderconfigured to decode an address to provide a plurality of word-linesignals, a plurality of output stages, each of the output stages (i)having an input coupled to the decoder to receive one of the word-linesignals and (ii) configured to turn off based on a first control signal,and control circuitry configured to pull gate voltages of transistors ofthe plurality of output stages to a low voltage, wherein the controlcircuitry is activated based on a second control signal.
 10. The memoryof claim 9, further comprising: a first power supply configured to powerthe decoder; and a second power supply, different than the first powersupply, configured to power the plurality of output stages.
 11. Thememory of claim 9, wherein each of the output stages includes (i) afirst transistor having a gate controlled by a first control signal, and(ii) an inverter coupled between the first transistor and a ground, thememory further comprising: pull-down circuitry coupled between the gatesof the first transistors and the ground and activated by a secondcontrol signal.
 12. The memory of claim 11, wherein the pull-downcircuitry comprises one or more second transistors coupled between thegates of the first transistors and the ground, each of the secondtransistors including a gate controlled by the second control signal.13. The memory of claim 12, wherein a number of the second transistorsis less than a number of the first transistors.
 14. The memory of claim11, wherein the first transistor comprises a PMOS transistor coupled tothe second power supply; and the inverter comprises (i) a second PMOStransistor coupled to the first PMOS transistor and having a gatecontrolled by the one of the word-line signals, and (ii) a first NMOStransistor coupled between the second PMOS transistor and the ground.15. The memory of claim 14, wherein the pull-down circuitry comprisesone or more second NMOS transistors coupled between the gates of thefirst transistor and the ground, the one or more second NMOS transistorshaving gates controlled by the second control signal.
 16. The memory ofclaim 9, wherein the decoder comprises a plurality of decoder logicmodules, each of the decoder logic modules being coupled to one or moreoutput stages of the plurality of output stages.
 17. A method foroperating a word-line driver, the method comprising: providing power toa decoder of the word-line driver using a first power supply; decodingan address using the decoder to generate word-line signals; transmittingthe word-line signals to a plurality of output stages of the word-linedriver, the plurality of output stages controlling voltage levels ofword lines based on the word-line signals and being powered by a secondpower supply that is different than the first power supply, wherein theplurality of output stages are turned off based on a first controlsignal; and activating pull-down circuitry of the word-line driver basedon a second control signal, the pull-down circuitry pulling gatevoltages of transistors of the output stages to a low voltage.
 18. Themethod of claim 17, wherein the plurality of output stages are turnedoff based on a first control signal, the method further comprising:activating pull-down circuitry of the word-line driver based on a secondcontrol signal, the pull-down circuitry pulling gate voltages oftransistors of the output stages to a low voltage.
 19. The method ofclaim 17, wherein the decoder is not turned off in a standby mode. 20.The method of claim 17, further comprising: turning on the plurality ofoutput stages when transitioning from a standby mode of operation to anactive mode of operation.